Presentation on theme: "OPTICAL ARCHITECTURES FOR MOBILE BACK- AND FRONTHAULING"— Presentation transcript:
1 OPTICAL ARCHITECTURES FOR MOBILE BACK- AND FRONTHAULING Thomas Pfeiffer, Frank Schaich - Alcatel-Lucent Bell Labs Stuttgart OFC/NFOEC wireless backhauling workshop - Los Angeles,
2 Backhauling or fronthauling ? EPC : Evolved Packet Core BBU : Baseband UnitRAN : Radio Access Networkcore networkmetro cell (200 m diam.)EPCcentralized BBUIP backhaulCPRI fronthaulmacro cell (1 km diam.)conventional RANcloud RANIP backhaul or CPRI fronthaul ?= conventional RAN or cloud RAN ? … most likely both of them
3 Choice of transmission technology : optical only Fiber transmission systemsprotocol : IP, CPRI, others (digital; RoF not considered here) direct or over PON, Ethernet, …multiplexing : TDM, WDM, TWDM, …topology : ptp, ptmp, ringarchitecture: dedicated ? overlay ? shared with FTTx ?Metricstechnical metrics :bandwidth (scaleability, user statistics), latency, jitterenvironmental factors : temperature, humidity, mechanicallocation factors : availability of local powering, footprint, accesseabilityeconomic metrics :infrastructure : ownership, availability of dark fibers, digging cost, leasing cost, opportunity for sharinglocation factors : power supply and power consumption, rights of way
4 Backhauling and fronthauling bandwidth in LTE IP peak bandwidth per sitetyp. for macro cellCPRI bandwidth per site* 8/15 in case of WCDMAtyp. for macro cellIP backhauling = variable bitrateantennas may be grouped (e.g. beamforming) : each group counts as one single element- user traffic statistics apply : shown above are achievable peak rates on air i/f avged. values may be less by an order of magCPRI fronthauling = constant bitrate - each antenna counts separately (individual streams) - 8B/10B can be removed for transport over Ethernetcompression can be applied to reduce to 1:3
5 Impact from traffic statistics Backhaul and fronthaul network dimensions and architecture shall account for traffic statisticstraffic statistics per cell statistical multiplex gain on IP backhaulvariations of total cell traffic over the day load sharing (pooling gain) in cloud RANtaken from Alcatel-Lucent Technology lightRadioTM White Paper „Economic analysis“ (2011)
6 Latency in LTE : limited by synchronous UL HARQ The allowed RRH eNB transmission time is limited to <<1 msec It comes at the expense of a reduced processing time in the eNBnOrig. TXn+4n+8NACK1st RTXUEeNBt [ms]3 msec fixed delay defined by LTE standardeNB processing1. PHY: UL frame decoding2. MAC: ACK/NACK creation3. PHY: DL frame creationnOrig. TXn+4n+8NACK1st RTXUEeNBreduced time for eNB processingt [ms]RRHround trip time (10 µsec / km) + transport system processing time
7 IP backhaul by 10G-PON : urban area, macro cells Serving area around traditional CO32 macro cells, backhauled by single dedicated 10G-PON peak rate = 10Gbps per site; sufficient even for extreme loads - average rate = 320 Mbps per site can be increased by using multiple 10G-PONs, WDM-stacked - link length = 20 km reaches any site within the area over realistic cable routesPossible migration towards serving from consolidated Super-COvia WDM stacking : hybrid WDM/TDM long reach 10G-PONs (cf. PIEMAN, MUSE, SARDANA for example architectures + upcoming NGPON2 standardisation for specs (tbd) )max. 20 kmpower splitterCentral OfficeeNBs14Router28OLTONTCOserving area: diam. 6 kmmacro cell: diam. 1 km
8 IP backhaul (ct‘d) : urban area, macro + metro cells Scenario: serving area around CO with32 macro cells: 10G peak / 320M avge. 10G-PON, 1:32 split (3 sectors * 8 antennas * 100 MHz) (XGPON1 or XGPON2)16 metros per macro : 1.7G peak / 26M avge. 8 x GPON, 1:64 split each (1 sector * 4 antennas * 100 MHz) (stacking via low cost WDM) low cost WDM-PON by cyclic wavelength allocation within 40 nm band cf. Pöhlmann, Pfeiffer: ECOC 2011, paper We.9.C.1COserving area: diam. 6 kmmacro cell: diam. 1 kmmetro cellsmax. 20 kmhybrid splitter: 10G - power splitter GPON - cyclic AWGCentral OfficeeNBs128metro (8 x 64)macro (32 x)10G-PONGPONmacro area16dipl exerpower splitterl 10G + lj GPON4RouterWDM1r (diplexer)GPON #1 … #810G PONcyclic AWGOLTs
9 Centralized processing : variants and benefits BBU clustering : move BBU hardware from BTS into common central spacesimplified hardware at antenna sites (footprint, electrical power) and in BBU (indoor specs)„zero latency“ links between BBUs allow for implementing CoMP and ICIC algorithmsBBU pooling : share hardware elements between multiple colocated BBUsadditional benefit : ease of load-sharing between clustersEither variant requires CPRI links to remote antenna sitestransmission bandwidths easily reach levels that render TDM-PON unattractivesmall split factors (1:2 or 1:4)constant bitrate, i.e. no statistical multiplex gainstrict latency limits (<<1 msec) require zero framing/buffering etc. delaysmost viable solutions employ ptp-links viafiber, if available …wavelength : ptp-WDM overlay on TDM-PON or „pure“ WDM-PON
10 CPRI fronthaul via WDM overlay on LR-PON (ACCORDANCE project) MCO … Metro Central OfficeRN … remote node
11 Enable BBU pooling, but not via CPRI : alternatives IP backhaulingcore networkEPCclassical eNBPDCP RLCRFMACPHYBIP variableincreased optical link bandwidthsplit within L2core networkEPCcentral unit (cluster)PDCP RLCMACslim eNBRFPHY≥ BIP variablesplit within L1core networkEPCcentral unit (cluster)PDCP RLCMACPHYextended RRHRFe.g. 0.2 * BCPRI fixedCPRI fronthaulingcore networkEPCcentral unit (cluster)PDCP RLCMACPHYCPRIRRHRFBCPRI fixed- simpler remote unit - possible pooling gains
14 Conventional Approach Example XG-PON1 upstream, 4 Wavelength Subbands SB1 – SB4 1260nm nm nm nm nmWavelength band is separated in four subbands for wavelength stackingRandomly distributed DFB laser wavelengths in the 20nm band1260nm nm nm nm nmDFB laser wavelength can be tuned by heating or cooling by ≈ 0.08nm/K. Tuning range up to 3nm.
15 TWDM 40/10G with ultra-low cost WDM upstream (ALU proposal, ECOC 2011) wavelength setsWSDM (wavelength set division multiplexing)Operational principle:- cyclic optical filter at Rx, 50 or 100 GHz gridnarrow range Tx tuneability instead of full bandaccomplished by integrated heater stripe (no TEC)otherwise conventional transmitter technologyDownstream : 4 x 10G TDM DWDM channels, 100GHz spacing, nm band- OLT : l-stabilised DFB transmitter- ONU : FP based tunable filterUpstream : 4 x 2.5G TDMA wavelength sets, 50GHz grid, nm band- OLT : filtered with cylical AWG- ONU : partially tunable DFB with integrated heater
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